Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2001-03-05
2003-05-27
Yamnitzky, Marie (Department: 1774)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S328000, C428S690000, C428S917000, C313S502000, C313S503000, C257S080000, C257S102000, C257S103000, C427S255180, C427S497000, C427S509000, C427S526000, C427S527000, C427S530000, C117S009000, C117S104000, C117S105000, C117S108000, C204S192100, C136S261000, C359S350000
Reexamination Certificate
active
06569534
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an iron silicide optical material which is used for optical interconnections for optical communications, optical sensors, and solar cells. The present invention also relates to an optical element using the optical material.
2. Description of the Related Art
There is growing demand for light-emitting elements and photo-receiving elements using material based on silicon so that these elements can be incorporated in a silicon substrate to be used in an optical sensor and for optical interconnections. A compound semiconductor such as, for example, gallium arsenide may be used as the material for the optical elements on the silicon substrate. However, it is difficult to incorporate such a compound semiconductor in the silicon substrate without causing defects in the structure of the compound semiconductor, and the resulting compound semiconductor exhibits poor thermal stability. Moreover, manufacturing of the compound semiconductor requires specific steps in addition to the conventional steps for manufacturing silicon integrated circuits, resulting in increased manufacturing costs. Accordingly, a technique for making silicon-based light-emitting and photo-receiving structures, which requires the conventional silicon-IC production process only, has been desired.
Conventionally, among the optical elements manufactured by the conventional technique, a light-emitting element containing iron silicide, operating at a suitable wavelength for silica glass optical fibers, which is approximately 1.5 &mgr;m, is known as a current-injection element (D. Leong, M. Harry, K. J. Reesen, and K. P. Homewood, “NATURE” Vol. 387, Jun. 12, 1997, pp. 686-688). This light-emitting element is fabricated by depositing an n-type silicon layer and a p-type silicon layer on a (100) oriented n-type silicon substrate by an epitaxial growth method, implanting iron ions in the p-type silicon layer in the vicinity of the p-n junction interface on the substrate, and annealing so as to form a monocrystalline layer of beta iron silicide (&bgr;-FeSi
2
) having an orthorhombic structure.
However, the above-described optical element containing iron silicide has an external quantum efficiency of approximately 0.1%, which is low and causes a problem. Moreover, the optical element emits a sufficient amount of light at a cryogenic temperature but not at room temperature. Several other studies made in regard to the light-emission characteristics of &bgr;-FeSi
2
show that the optical element exhibits a long luminescence decay time, i.e., approximately several ten of microseconds. Optical interconnections and optical communications require much shorter luminescent decay time.
In view of the above, the present inventors have proposed a luminescent substance in which semiconductor particles of &bgr;-FeSi
2
, having a particle diameter on the order of nanometers, are dispersed in p-type or n-type amorphous silicon or p-type or n-type amorphous silicon carbide (Japanese Unexamined Patent Application Publication No. 11-340499). Since the &bgr;-FeSi
2
semiconductor particles having the particle diameter on the order of nanometers are crystallized and are dispersed in the amorphous silicon or in the amorphous silicon carbide having a large bandgap, injected carriers are confined inside the semiconductor particles, thereby enhancing the light-emission efficiency compared to the conventional monocrystalline &bgr;-FeSi
2
.
Among conventional photo-detectors, a variety of solar-cell elements, such as a single crystal silicon type, a polycrystalline silicon type, an amorphous silicon (a-Si) type, and a gallium arsenide (GaAs) type are available on the market. However, these solar-cell elements have problems with regard to their cost and conversion efficiency, and a photo-receiving material having higher efficiency at low cost is desired. The &bgr;-FeSi
2
has a significantly large optical absorption coefficient at a wide wavelength range for sunlight, and can be manufactured as an ultra thin film. Thus, when the &bgr;-FeSi
2
is used as a photo-detector of a solar cell, the amount of raw material used can be reduced and the costs can be decreased.
The luminescent substance disclosed in the above-described Japanese Unexamined Patent Application Publication No. 11-340499 can still be improved from the point of view of light-emission efficiency and the efficiency of the manufacturing method.
Moreover, because &bgr;-FeSi
2
has a carrier mobility which is too small for use as a material for the photo-receiving material of solar cells, &bgr;-FeSi
2
is yet to be applied to solar cells.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a silicon-based optical material capable of achieving high light-emission efficiency and high photo-receiving efficiency.
Another object of the present invention is to provide an optical material which is capable of achieving a luminescent decay time of several tens of nanoseconds or less and which can be applied to high-speed optical communications.
Still another object of the present invention is to provide an optical material which emits and receives light at room temperature.
Yet another object of the present invention is to provide an optical element using the above-described optical material.
To these ends, the present invention provides an optical material according to an aspect of the invention comprising a crystalline silicon and Fe
x
Si
2
in the form of dots, islands, or a film. The Fe
x
Si
2
has a symmetrical monoclinic crystalline structure belonging to the P2
1
/c space group and is synthesized at the surface or in the interior of the crystalline silicon. The monoclinic structure corresponds to a deformed structure of &bgr;-FeSi
2
generated by heteroepitaxial stress between the {110} plane of the Fe
x
Si
2
and the {111} plane of the crystalline silicon, wherein the value of x is 0.85≦x≦1.1.
Because the &bgr;-FeSi
2
is artificially deformed and the crystalline structure thereof is changed from an orthorhombic crystal to a monoclinic crystal, the &bgr;-FeSi
2
becomes less symmetrical. Thus, dipole transitions are allowed between many electronic states, and the oscillator strength which determines characteristics of the light-emitting/photo-receiving material is larger than that of the &bgr;-FeSi
2
.
Preferably, the lattice constant of the c axis of the Fe
x
Si
2
having the monoclinic crystalline structure is 7.68±0.20 Å, which is equal to the interatomic distance of the {111} plane of the crystalline silicon, the lattice constant of the a axis of the Fe
x
Si
2
is 10.17±0.35 Å, the lattice constant of the b axis of the Fe
x
Si
2
is 7.75±0.35 Å, and the angle defined by the a axis and the b axis of the Fe
x
Si
2
is 95±3°. This crystalline structure is hereinafter referred to as “&bgr;′-I”.
Preferably, the thickness of the Fe
x
Si
2
having the monoclinic crystalline structure is 5 to 2,000 Å. In this manner, the Fe
x
Si
2
can maintain the monoclinic crystalline structure. This crystalline structure is hereinafter referred to as “&bgr;′-I”.
The optical material may further comprise &bgr;-FeSi
2
having an orthorhombic crystalline structure. The total thickness of the Fe
x
Si
2
and the &bgr;-FeSi
2
is preferably 200 to 10,000 Å.
In this manner, the thickness of the layer can be increased compared to the optical material comprising Fe
x
Si
2
only and the optical material can be easily manufactured. Also, because of the monoclinic crystals, light-emitting intensity and photo-receiving efficiency can be improved compared to the optical material using only &bgr;-FeSi
2
. When the thickness exceeds 10,000 Å, all the crystals will change to &bgr;-FeSi
2
.
Another aspect of the present invention provides an optical element comprising one of a light-emitting layer and a photo-receiving layer comprising the above-described Fe
x
Si
2
. The crystalline silicon is of
Mizushima Kazuki
Yamaguchi Kenji
Mitsubishi Materials Corporation
Yamnitzky Marie
LandOfFree
Optical material and optical element using the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical material and optical element using the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical material and optical element using the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3005680